Permanent magnet motors energized from an alternating current source are well-known. Also, it is well-known to utilize various types of couplings from the rotors of such motors. One type of coupling is a hysteresis, drag cup type of coupling. In the typical unit, multiple magnetic structures are required and the output torque from the coupling normally is fixed.
Providing a motor with a variable output coupling has been very expensive, due to the complexity of the structures involved. These structures have had limited control of the torque available from the related coupling.